Protectors for electric circuits



1961 M. R. SMITH 3,011,038

PROTECTORS FOR ELECTRIC CIRCUITS Filed Jan. 8, 1960 o o q I a l t INVENTOe MART/N 1? SM! TH portion of the fuse of H68. 1 and 2,

3,011,038 Patented Nov. 28, 1 961 3,011,033 PROTECTORS FOR ELECTRIC CIRCUITS Martin R. Smith, St. Louis, Mo., assignor to McGraw- Edison Company, Elgin, 111., a corporation of Delaware Filed Jan. 8, 1960, Ser. No. 1,253 I Claims. (Cl. 200-120) I This invention relates to improvements in protectors for electric circuits. More particularly, this invention relates to improvements in electric fuses.

. It is therefore an object of the present invention to provide an improved electric fuse.

The ratings of electric fuses are affected by the temperatures rises permitted for those fuses; and it would be possible to increase the rating of an electric fuse if that fuse could be made to operate with a lesser temperat-ure rise. The present invention provides such a fuse; and it does so by grouping the fusible elements of the fuse so they define an annulus. By grouping the fusible elements so they define an annulus, the present invention reduces the overall reactance of the fuse. This reduction in overall reactance reduces the heat generation due to reactance; and hence the fuse will have a lesser temperature rise. By grouping the fusible elements of the fuse so they define an annulus, the present invention also makes it possible to leave the central area of the fuse open and thereby facilitates the dissipation of heat from that central area. That heat dissipation also enables the fuse to have a lesser temperature rise. As a result, the fuse provided by the present invention can be given a larger ampere rating. It is therefore an object of the present invention to provide an electric fuse which has the fusible elements thereof grouped so they define an annulus.

The lesser temperature rise provided by the present invention can, if desired, be utilized to permit the use of fewer fusible elements. The use of a lesser number of fusible elements enables the fuse to be facter acting; and, in many instances, a faster acting fuse is desirable. Consequently, the lesser temperature rise provided by the present invention makes it possible to increase the ampere rating of the fuse or makes it possible to make the fuse faster acting.

Other and further objects and advantages of the present invention should be come apparent roman examination of the drawing and accompanying description.

In the drawing and accompanying description a preferred embodiment of the present invention is shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention. and that the invention will be defined by the appended claims.

In the drawing,

FIG. 1 is a plan view of one embodiment of fuse that is made in accordance with the principles and teachings of the present invention,

FIG. 2 is a viewof the right-hand end shown in FIG. 1,

FIG. 3 is a longitudinal section through the central of the fuse I FIG. 4 is a view of the inner end of one of the end bells of the fuse of FIGS. 1-3, and FIG. 5 is a sectional "iew through the end bell of FIG. 4, and itzis taken along the plane indicated by the y line5-5 in HG. 4.

States Patent Ofiice 7 Referring to the drawing in detail, the numeral 10 denotes one of the end bells of a fuse that is made in accordance with the principles and teachings of the present invention. That end bell has a flat terminal 12 secured to it. Theterminal 12 and the end bell 10 could be cast integrally or they could be suitably integrated by brazing, silver soldering, or the like. The terminal 12 has a number of openings 14 throughit, and those openings can accommodate bolts or other fasteners which can be used to secure the terminal 12 to a bus bar or other conductor. The end bell 10 has a circular opening 16 at the center. thereof, and that opening is spanned by a portionof the inner end of the terminal 12. That portion of the inner end of the terminal 12 which spans the opening 16 has a reduced thickness; and that reduced thickness portion is connected to the full thickness portion of the inner end of the terminal 12 by fillets. The reduced thickness portion of the inner end of the terminal 12 coacts with the opening 16 in end bell 10 to permit free movement ofair through the central opening 16 of the end bell 10. i

The inner face of the end bell 10 has a number of radially-directed recesses 20 formed in it; and those recessesa're arranged in two annular bands. Those recess'esare shallow, and they are rectangular incontiguration. The recesses 20 in the outer annular band are staggered relative to the recesses 20 in the inner annular band. An annular recess 22 is provided in the end bell 10 adjacent the circular opening 16. That recess is deeper and wider than any of the recesses 20.

The numeral 26 denotes the other end bell for the fuse,:and thatend bell is identical to the first end bell. A terminal 28 is provided for the end bell 26, and that terminal can be cast integrally with that end hell or can be subsequently integrated with it. The terminal 28 has openings 30 therein, and those openings will accommodate bolts or other fasteners to secure that terminal to a bus bar orother conductor. A circular opening 32 is provided at the center of the end bell 26, and a portion 34 of the inner end of the'terminal 28 spans that opening. The portion 34 of the inner end of the terminal 28 has a reduced thickness, as shown particularly by FIG. 5. The reduced thickness portion 34 is connected to the full width portion of the inner end of the terminal 28 by fillets.

The numeral 36 denotes radially-directed.shallow recesses which are formed in the inner face of the end bell 26. Those recesses are arranged in two annular-bands, and each of those recesses is rectangular. The recesses in the outer annular band are staggered relative to the recessesin the inner annular band. An annular recess with the recesses 20 in the end bell 10. Similarly, the.

- annular recess 38 is in register with the annular recess 22 in the end bell 10. V

The recesses 22 and 38 accommodate the opposite ends of an inner casing 42. That casing is tubular, and it will preferably be made of a non-conducting material. An outer casing 44 of non-conducting material telescopes over the peripheries of the end bells 10 and 26. The end bells 10 and 26 will confine and hold the inner casing 42, but fasteners, not shown, .will preferably be used to secure the outer casing 44 to the end bells 10 and 26.

3 Preferably, those fasteners will take the form of pins or threaded members which pass through radially-directed openings in the outer housing 44 and seat in radiallydirected holes in the end bells and 26.

Fusible elements 48, which are provided with openings 50, are disposed between and are electrically connected to the end bells 10 and 26. The left-hand ends of the fusible elements 48 are disposed within the recesses 20 of end bell 10, and the right-hand ends of those fusible elements are disposed within the recesses 36 of end bell 26. Solder, not shown, is used to bond those ends to those end bells. The fusible elements 48 are thin, and hence none of them is very strong. However, the fusible elements 48 collectively provide a firmer connection between the end bells 10 and 26. An arc-quenching filler material will usually be used to imbed the fusible elements 48.

The inner casing 42 defines an open central area, and that area communicates with the ambient atmosphere through the openings 16 and 32 in the end bells 10 and 26, respectively. As a result, heat which passes into that open central area by passing inwardly through the wall of the inner casing 42 will be dissipated into the air within that area and will then be carried away to the ambient atmosphere. This is particularly true where the fuse has its long axis set vertically, because the inner casing 42 will act as a chimney and enable convection currents to keep air moving upwardly through that central area. This dissipation of heat is desirable because it enables the fuse to operate with a lower temperature rise.

The fact that the fusible elements 48 are arranged in two annular bands and are thus spaced outwardly from the center of the fuse also helps reduce the temperature rise of the fuse. This is due to the fact that the fuse has less reactance than does a fuse which has the same number of fusible elements but has those fusible elements distributed uniformly across the inner faces of the end bells of the fuse.

The openings 50 in the fusible elements 48 form weak spots for the fusible elements 48, and those weak spots enable those fusible elements to blow and protect the circuit. If desired, masses of heat softenable material could be mounted within one of the openings 50 in the fusible elements 48, and those masses of heat softenable material would tend to alloy with the metal of the fusible elements 48 and thereby foster blowing of the fuse on long continued, relatively-low overloads.

This invention can be used with fuses having different ampere ratings. However its value is most pronounced where it is used with fuses having ampere ratings in excess of one thousand amperes.

Whereas the drawing and accompanying description have shown and described one preferred embodiment of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention Without affecting the scope thereof.

' What I claim is:

1. A protector for electric circuits that has electrically conductive end bells, an electrically conductive terminal that projects outwardly from the outer face of one of said end bells, a second electrically conducting terminal that projects outwardly from the outer face of the other i of said end bells, each of said end bells being circular in configuration, each of said end bells having a circular opening at the geometric center thereof, the first said terminal having a portionthat spans the circular opening in said one end bell, said second terminal having a portion that spans the circular opening in said other end bell, the opening-spanning portion of each of said terminals being of reduced thickness to facilitate the passage of air through said circular openings, fillets connecting said opening-spanning portions of said terminal with the rest of said terminals, a plurality of rectangular radially-directed recesses in the inner faces "of said end bells, said 4- recesses being grouped in two annular bands, the recesses in one of said annular bands being staggered relative to the recesses in the other of said annular bands, the recesses in said annular bands being in register with each other, electrically conductive fusible elements that have the left hand ends thereof disposed in the recesses in said annular bands in said one end bell and having the right-hand ends thereof disposed in the recesses in said annular bands in said other end bell, each of said end bells having an annular recess in the inner face thereof, said annular recesses being disposed inwardly of said annular bands and being contiguous with said circular openings, a nonconducting tube that has its left-hand end disposed in the annular recess in said one end bell and that has its righthand end disposed in the annular recess in said other end bell, said tube closing and sealing the innermost portion of an annular area defined by said end bells, a second non-conducting tube that telescopes over and is supported by the outer peripheries of said end bells and that closes and seals the outermost portion of said annular area defined by said end bells, solder that bonds said fusible elements to said end bells, and arc-quenching filler that is within said annular space and that imbeds said fusible elements, said fusible elements generating heat whenever current flows through said protector for electric circuits and responding to predetermined overloads to blow and open the circuit, the heat from said fusible elements being dissipated by said end bells and by the first said and said second tubes.

2. A protector for electric circuits that has end bells, a terminal that projects outwardly from the outer face of one of said end bells, a second terminal that projects outwardly from the outer face of the other of said end bells, each of said end bells having a circular opening at the geometric center thereof, the first said terminal having a portion that spans the circular opening in said one end bell, said second terminal having a portion that spans the circular opening in said other end bell, the opening-spanning portion of each of said terminals being of reduced thickness to facilitate the passage of air through said openings, a plurality of recesses in the inner faces of said end bells, said recesses being grouped in two annular bands, the recesses in one of said annular bands being staggered relative to the recesses in the other of said annular bands, the recesses in said annular bands being in register with each other, fusible elements that have the left-hand ends thereof disposed in the recesses in said annular bands in said one end bell and having the righthand ends thereof disposed in the recesses in said annular bands in said other end bell, each of said end bells having an annular recess in the inner face thereof, said, annular recesses being contiguous with said circular openings, a non-conducting casing that has its left-hand end disposed in said annular recess in said one end bell and that has its right-hand end disposed in the annular recess in said other end bell, said casing closing the innermost portion of an annular area defined by said end bells, a second non-conducting casing that telescopes over and is supported by the outer peripheries of said end bells and that closes the outermost portion of said annular area defined by said end bells, solder that bonds said fusible elements to said end bells, and arc-quenching filler that iswithin said annular space and that imbeds said fusible elements, said fusible elements generating heat whenever current flows through said protector for electric circuits and responding to predetermined overloads to blow and open the circuit, the heat from said fusible elements being dissipated by said end bells and by the first said and said second casings.

3. A protector for electric circuits that has end bells, a terminal that projects outwardly from one of said end bells, a second terminal that projects outwardly from the other of saidend bells, each of said end bells having an opening adjacent the center thereof, the first said terminal having a portion that spans the opening in said one end bell, said second terminal having a portion that spans the opening in said other end bell, the opening-spanning portion of each of said terminals being of reduced thickness to facilitate the passage of air through said openings, a plurality of recesses in the inner faces of said end bells, said recesses being grouped in annular bands, the recesses in said annular bands eing in register with each other, fusible elements that have the left-hand ends thereof disposed in the recesses in said annular bands in said one end bell and having the right-hand ends thereof disposed in the recesses in said annular bands in said other end bell, each of said end bells having an annular recess in the inner face thereof, a non-conducting casing that has its left-hand end disposed in the annular recess in said one end bell and that has its right-hand end disposed in the annular recess in said other end bell, said casing closing the innermost portion of an annular area defined by said end bells, a second non-conducting casing that telescopes over and is supported by the outer peripheries of said end bells and that closes the outermost portion of said annular area defined by said end bells, and solder that bonds said fusible elements to said end bells, said fusible elements generating heat whenever current flows through said protector for electric circuits and responding to predetermined overloads to blow and open the circuit, the heat from said fusible elements being dissipated by said end bells and'by said casings.

4. A protector for electric circuits that has end bells, a terminal that projects outwardly from one of said end bells, a second terminal that projects outwardly from the other of said end bells, each of said end bells having an opening therein, the first said terminal having a portion that spans the opening in said one end bell, said second terminal having a portion that spans the opening in said other end bell, a plurality of fusible elements that have the left-hand ends thereof adjacent said one end bell and having the right-hand ends thereof adjacent said other end bell, a non-conducting tubular casing that has its lefthand end adjacent said one end bell and that has its righthand end adjacent said other end bell, said casing closing the inner portion of an area defined by said end bells but constituting an air passage with heat-transferring walls, a second non-conducting casing that has its ends adjacent said end bells and that closes the outer portion of said area defined by said end bells, and solder that bonds said fusible elements to said end bells, said fusible elements generating heat whenever current flows through said protector for electric circuits and responding to predetermined overloads to blow and open the circuit, the heat from said fusible elements being dissipated by said end bells and by said casings and by the air issuing from the first said casing.

5. A protector for electric circuits that has end bells, a terminal that projects outwardly from one of said end bells, a second terminal that projects outwardly from the other of said end bells, each of said end bells having an opening therein, fusible elements that have the lefthand ends thereof connected to said one end bell and having the right-hand ends thereof connected to said other end bell, a non-conducting tubular casing that has its left-hand end in engagement with said one end bell and that has its right-hand end in engagement with said other end bell, said casing closing the inner portion of an area defined by said end bells butconstituting an air passage with heat-transferring Walls, and a second non conducting casing that engages said end bells and that closes the outer portion of said area defined by said end bells, said fusible elements generating heat whenever current flows through said protector for electric circuits and responding to predetermined overloads to blow and open the circuit, the heat from said fusible elements being dissipated by said end bells and by said casings and by the air issuing from the first said casing.

6. A protector for electric circuits that has end bells, each of said end bells having an opening therein, fusible elements that have the left-hand ends thereof adjacent one of said end bells and having the right-hand ends thereof adjacent the other end bell, a non-conducting tubular casing that has its left-hand end adjacent said one end bell and that has its right-hand end adjacent said other end bell, said casing closing the inner portion of an area defined by said end bells but constituting an air passage with heat-transferring walls, a second non-conducting casing that has its ends adjacent said end bells and that closes the outer portion of said area defined by said end bells, and solder that bonds said fusible elements to said end bells, said fusible elements generating heat whenever current flows through said protector for electric circuits and responding to predetermined overloads to blow and open the circuit, the heat from said fusible elements being dissipated by said end bells and by said casings and by the air issuing from the first said casing.

7. A protector for electric circuits that has end bells, each of said end bells having an opening therein adjacent the geometric center thereof, fusible elements that have the left-hand ends thereof adjacent one of said end bells and having the right-hand ends thereof adjacent the other end bell, a non-conducting tubular casing that has its left-hand end adjacent said one end bell and that has its right-hand end adjacent said other end bell, said casing closing the inner portion of an area defined by said end bells but constituting an air passage with heat-transferring walls, a second non-conducting casing that has its ends adjacent said end bells and that closes the outer portion of said area defined by said end bells, arc-quenching filler that is within said area and that imbeds said fusible elements, and solder that bonds said fusible elements to said end bells, said fusible elements generating heat whenever current flows through said protector for electric circuits and responding to predetermined overloads to blow and open the circuit, the heat from said fusible elements being dissipated by said end bells and by said casings and by the air issuing from the first said casing.

8. A protector for electric circuits that has end bells, each of said end bells having a circular opening therein, each of said end bells being circular, fusible elements that have the left-hand ends thereof adjacent one of said end bells and having the right-hand ends thereof adjacent the other end bell, an annular recess in each of said end bells, said annular recesses being in register with each other, a non-conducting tubular casing that has its left-hand end disposed in the annular recess in said one end bell and that has its right-hand end disposed in the annular recess in said other end bell, said casing closing the inner portion of an area defined by said end bells but constituting an air passage with heat-transferring walls, a second nonconducting casing that has its ends telescoped over said end bells to close said area defined by said end bells, and solder that bonds said fusible elements to said end bells, said fusible elements generating heat whenever current flows through said protector for electric circuits and responding to predetermined overloads to blow and open the circuit, the heat from said fusible elements being dismeeting the left-hand ends of said heat-generating fusible elements, a second member interconnecting the righ -hand ends of said heat-generating fusible elements, each of said members defining an open area, said heat-generating fusible elements being secured to said members and being grouped around said open area, said open area facilitating the dissipation of heat from said heat-generating fusible elements, an outer housing that helps define said open area, and an inner housing that helps define said open area and that constitutes an air passage with heat-transferring walls.

10. A protector for electric circuits that has a plurality of heat-generating fusible elements, an end bell interconnecting the left-hand ends ofsaid heat-generating fusible elements, a second end bell interconnecting the right-hand ends of said heat-generating fusible elements, each of said end bells being circular, each of said end bells having a circular opening at the center thereof, said heat-generating fusible elements being electrically bonded to said end bells and being disposed outwardly of said circular openings, said circular openings facilitating the dissipation ofheat from said heat-generating fusible elements, an outer housing that overlies and helps confine said heat-generating fusible elements, and an inner housing that underlies and helps confine said heat-generating fusible elements and 10 that constitutes an air passage With heat-transferring Walls.

References Cited in the file of this patent UNITED STATES PATENTS 

